Single-component, moisture-curing polyurethane compositions have been used as adhesives, sealants, and coatings. For the application as sealants for expansion joints on structures, compositions are used that cure without forming bubbles and are flexible after their curing in a broad temperature range; i.e., in the low expansion range, they have the lowest possible values for the tensile stress and at the same time have a high shape recovery. As a result, such sealants are able to supplement expansion or compression of the joints that is induced by movements or temperature differences in a reversible manner and with low power transmission to the joint substrates and thus to stress or to damage the latter as little as possible.
Single-component polyurethane compositions that contain long-chain polyaldimines and that are suitable as flexible sealants are known from WO 2007/104761 A1. The compositions that are described cure without forming bubbles and have low values for 100% tensile stress both at room temperature and at −20° C. Like other flexible polyurethane compositions, they also tend to form a more or less strongly adhesive surface, which easily becomes dirty, during curing, however. Expansion joints in the outside area of structures are in most cases readily visible to the observer and are matched in color to the front of the building. They often have, moreover, a bright color tone, such as white, light gray, or concrete gray; their soiling is thus often quickly visible and therefore distracting.
Single-component polyurethane compositions that contain special polyaldimines, which are suitable as sealants that do not tend to get dirty, are known from WO 2008/116900 A1 and WO 2008/116902 A1. The compositions that are described have a low surface adhesiveness after curing but do not show any anisotropic material properties.
Polyurethane compositions that contain at least one polyurethane prepolymer that has isocyanate groups, at least one catalyst that accelerates the reaction of NCO groups with water, and at least one compound that contains at least one α-silane group and that are suitable as adhesives for gluing in car windows are known from WO 2006/130592 A1. The described compositions do not show any anisotropic material properties, however.